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IC 


9055 



Bureau of Mines information Circular/1985 



Corrosion of Roof Bolt Steels in Missouri 
Lead and Iron Mine Waters 

By M. M. Tilman, A. F. Jolly III, and L. A. Neumeier 




UNITED STATES DEPARTMENT OF THE INTERIOR 



751 

1f/NES 75TH A^"^ 



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{^umi mJi4 , ^-^ i¥^) 



Information Circular 9055 

A 

Corrosion of Roof Bolt Steels in Missouri 
Lead and Iron Mine Waters 

By M. M. Tilman, A. F. Jolly III, and L. A. Neumeier 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Model, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



iii!iaji<«-;3' if.WitS^^iSMW 



-w^ 



z 



^5 






Library of Congress Cataloging in Publication Data: 




Tilman, IVl. M. (Milton M.) 

Corrosion of roof bolt steels in Missouri lead and iron mine waters. 

(Bureau of Mines information circular ; 9055) 

Bibliography: p. 9. 

Supt. of Docs, no.: I 28.27: 905 5. 

1. Mine roof bolting. 2. Rock bolts — Corrosion. 3. Mine waters. 
4, Lead mines and mining— Mi ssouri. 5. Iron mines and mining— Mis- 
souri. I. Jolly, A. F. (A. Fletcher). II. Neumeier, L. A. III. Title. 
IV. Scries: Information circular (United States. Bureau of Mines) ; 9055. 



TN295.U4 [ TN289.31 622s[622\28] 85-600221 



li 



5J- 
0- 

00 

'^ 
-^ CONTENTS 

^ Page 

Abstract. 1 

Introduction 2 

Experimental procedure, 2 

Results and discussion 4 

Conclusions 8 

References 9 

ILLUSTRATIONS 

1 . Example of anodic polarization plot 5 

2. Example of cathodic polarization plot 5 

3. Example of polarization resistance (linear polarization) plot 6 

4. Example of derived electrochemical corrosion rate versus stabilization 

time 6 

5. Example of pitting scan showing little tendency of specimen to pit 7 

6. Example of pitting scan indicating tendency of specimen to pit 7 

TABLES 

1. High-strength, low-alloy steel compositions 4 

2. Analyses of mine waters from Missouri lead and iron mines 5 

3. Electrochemically detemnined corrosion rates. 6 

4. Corrosion rates determined by weight-loss method 7 

5. Pitting tendency of HSLA and galvanized steels in Missouri mine waters..,. 8 





UNIT OF MEASURE ABBREVIATIONS USED IN 


THIS REPORT 


°F 


degree Fahrenheit nA/cm^ 


nanoampere per square 
centimeter 


h 


hour 






ppm 


part per million 


in 


inch 






V 


volt 


min 


minute 






wt pet 


weight percent 


mL 


milliliter 




mpy 


mil per year 





aHi 



CORROSION OF ROOF BOLT STEELS IN MISSOURI LEAD AND IRON MINE WATERS 

By M. M. Tilman, ^ A. F. Jolly lll,2and L. A. Neumeier^ 



ABSTRACT 

As part of ongoing research to improve mine safety, the Bureau of 
Mines conducted research on the corrosion of friction rock stabilizer 
steels in five Missouri lead and iron mine waters. Electrochemical cor- 
rosion tests, including evaluation of pitting tendency, were performed 
on two types of high-strength, low-alloy (HSLA) steels and galvanized 
steel in four Missouri lead mine waters and one Missouri iron mine wa- 
ter. The tests were conducted at in-mine water temperatures in both 
air-saturated and deaerated waters. Static, weight-loss corrosion tests 
were also conducted on HSLA steel specimens in the five Missouri mine 
waters for 2,900-h duration at average In-mine water temperatures and 
air-dissolved oxygen contents of 6 to 7 ppm. Corrosion rates determined 
by the weight-loss tests were roughly comparable with rates determined 
electrochemically in deaerated waters containing 0.3 to 0.5 ppm dis- 
solved oxygen content. Passivation of specimen (nongalvanized) surfaces 
in air-saturated waters resulted in very low electrochemically deter- 
mined corrosion rates. Pitting tendency was generally higher for both 
HSLA steels in air-saturated waters than in deaerated waters. Gal- 
vanized steel generally exhibited higher tendency to pitting in the de- 
aerated waters than in the aerated mine waters. 



^Metallurgist (retired). 
^Metallurgist. 
■^Supervisory metallurgist. 
Rolla Research Center, Bureau of Mines, Rolla, MO. 



..'^-^i^.'--H£:»'.:'>;'&3£!3«iui»«eB^3i!iSS^i<t^iijai^S^y^!^^S^ 



INTRODUCTION 



In the late 1970' s, a different concept 
in roof-rock bolts was introduced commer- 
cially in friction rock stabilizers. 
Several types of the stabilizers have 
been developed and are in commercial use. 
They are thin-wall tubular devices which, 
unlike point-anchor bolts, exert their 
holding power by compressive forces act- 
ing over the length of the stabilizer. 
Because of their unique holding mechan- 
ism, the stabilizers are claimed to be 
particularly useful in softer rock such 
as sandstone and shale. However, because 
of the relatively thin wall, they are 
more vulnerable to corrosion, which can 
under certain conditions cause a serious 
loss of strength in a relatively short 
time. Friction rock stabilizers are nor- 
mally not recommended for use where par- 
ticularly long-term support is required. 

The Split Set4 stabilizer has gained 
wide acceptance in the metal mining in- 
dustry. Over 25 million Split Set sta- 
bilizers have been installed, primarily 
in metal mines, not only in the United 
States but also in approximately 30 
foreign countries. The Split Set sta- 
bilizer is a slotted tube 1-1/2 in or 
larger in diameter, which is forced into 
an undersize hole, with the result that 
compressive forces act over the entire 
length of the tube. The stabilizers are 
made of steel sheet nominally about 0.1 
in thick and are produced in various 
lengths. Although a device has been de- 
veloped to check for proper installation 
of Split Set stabilizers (9^),^ no tech- 
nique has been developed for revealing 
loss of strength after installation, such 
as that due to corrosion. Two types of 
high-strength, low-alloy (HSLA) steels 



are used to manufacture Split Set sta- 
bilizers. Hot-dip-galvanized Split Set 
stabilizers are also available. 

Research was previously conducted by 
the Bureau of Mines on the corrosion 
resistance of Split Set stabilizers in 
copper and uranium mine waters (11). 
Results of the prior research indicated 
that galvanized steel, not surprisingly, 
was far superior to the unprotected steel 
in general corrosion resistance. For the 
waters evaluated, limited corrosion tests 
indicated little tendency to pitting 
of galvanized, steel compared to that 
for the uncoated steel. Copper-bearing 
HSLA steel was shown to be slightly 
more corrosion resistant than non-copper- 
bearing HSLA steel. Equations were de- 
veloped relating dissolved oxygen, chlo- 
ride, sulfate, and magnesium contents of 
the mine waters to corrosion rates of two 
nongalvanized HSLA steels. An equation 
was developed relating dissolved oxygen 
content and mine water temperature to 
corrosion rate of galvanized steel. The 
research indicated the need for preven- 
tion and control of corrosion of the roof 
support members in view of the considera- 
ble variables involved in prediction of 
corrosion damage. 

The work with Missouri mine waters de- 
scribed in this report is an extension of 
the previous research on corrosion of 
Split Set stabilizers in Western mine wa- 
ters and is part of the Bureau's ongoing 
program to improve mine safety. Results 
of the work are intended to aid Mine 
Safety and Health Administration and min- 
ing industry personnel in better predict- 
ing safe installation periods of friction 
rock stabilizers. 



EXPERIMENTAL PROCEDURE 



The Ingersoll-Rand Corp. provided sheet 
samples of EX-TEN-H60 and KAI-WELL-55, 
the two high-strength, low-alloy (HSLA) 



'Registered trademark of Ingersoll-Rand 



Co. 



■'Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



steels from which Split Set stabilizers 
are manufactured, for use in the corro- 
sion experiments. Samples of the steels 
were analyzed for comparison with speci- 
fications. Microstructures of the steels 
were shown in a previous report (11). 
Galvanized plain-carbon steel sheet 
(flat) , obtained from a commercial sup- 
plier, was used for corrosion testing 



instead of galvanized Split Set stabiliz- 
er steel, because galvanized Split Set 
sheet stock was not readily available. 
Corrosion samples cut from galvanized 
stabilizers were incompatible with the 
corrosion test equipment because of their 
curvature; the specimen holder would only 
accept flat specimens for a proper fit. 
Attempts to flatten the galvanized stabi- 
lizer samples damaged the galvanized sur- 
face. The use of plain-carbon galvanized 
steel sheet was deemed acceptable, since 
variation in composition of the outer 
zinc layer of galvanized coatings, if 
present, has been indicated to be insig- 
nificant with respect to detrimental cor- 
rosion effects (2^, p. 712; _3, p. 646). 
The scope of the research did not extend 
to the complex condition in which corro- 
sion might, with extended time, proceed 
to penetrate the zinc coating. It should 
be mentioned that, even in that eventual- 
ity, the zinc continues to provide sacri- 
ficial protection to steel until consid- 
erable steel is exposed (2_, p. 712). 

A Swellex6 bolt, another type of fric- 
tion rock stabilizer, was provided by 
personnel at a western mine. A section 
of the bolt was flattened, corrosion sam- 
ples punched, and the steel analyzed. 

Five-gallon water samples were obtained 
from four Missouri lead mines and one 
Missouri iron mine. The lead mines were 
the Fletcher Mine, Indian Creek Mine, and 
St. Joe #28 Mine, of St. Joe Lead Co., 
and the Magmont Mine, of Cominco Ameri- 
can/Dresser Industries. The iron mine 
was the Pea Ridge Mine of Pea Ridge Iron 
Ore Co. Mine water temperatures were 
measured at the sampling site. The sam- 
ples were analyzed for common elements, 
and the pH values were measured. The 
Langelier (saturation) indices, which 
indicate the relative tendency for CaC03 
to precipitate from water and form a 
protective deposit, were calculated using 
the values for the total dissolved 
solids, calcium and HCO3 contents, and pH 
and temperature. Corrosion rates of EX- 
TEN-H60 and KAI-WELL-55 steels were mea- 
sured by both electrochemical and weight- 
loss methods in all five mine waters. 
Corrosion rates of galvanized steel were 

^Registered trademark of Atlas Copco. 



measured in the five mine waters by 
electrochemical methods only. Corrosion 
rates of the Swellex steel were measured 
electrochemically in air-saturated and 
deaerated water from the St. Joe #28 lead 
mine. 

A commercial corrosion measurement sys- 
tem (10) , consisting of a corrosion cell 
and microprocessor unit, was used to ob- 
tain "instantaneous" corrosion rates. In 
operation, the corrosion cell containing 
test solution, specimen, counter elec- 
trodes, and standard calomel reference 
electrode is immersed in a controlled- 
temperature water bath. The micropro- 
cessor unit, correctly programmed and 
with appropriate operator skill, calcu- 
lates corrosion rates based on the corro- 
sion current. Tafel constants obtained 
in anodic and cathodic polarization plots 
are used in a subsequent polarization re- 
sistance plot to calculate the general 
corrosion rate. A more detailed discus- 
sion of the electrochemical test equip- 
ment and technique may be found in a pre- 
vious Bureau report (11). Discussions of 
electrochemical measurement of corrosion 
rates are found in several references (_1^, 
4, 6, 8). Corrosion rates were deter- 
mined electrochemically in both helium- 
degassed (deaerated) and air-saturated 
(aerated) mine waters at the measured in- 
mine water temperature. 

In addition to corrosion rate deter- 
minations, pitting susceptibility scans 
were run on each steel in all except one 
mine water. The pitting scans were run 
in both deaerated and air-saturated wa- 
ters at the in-mine water temperature. 

Test specimens of the HSLA steels were 
ground over 600-grit SiC abrasive paper, 
ultrasonically cleaned in ethanol, and 
dried in a warm air blast. Galvanized 
specimens were prepared with the same 
procedure, except that grinding was omit- 
ted. After immersion in deaerated test 
solutions, the specimens were electrolyt- 
ically cleaned by operating the cell with 
the specimen as cathode [-1.0 V vs stan- 
dard calomel electrode (SCE)] for 1 rain 
immediately preceding the test run. Spe- 
cimens tested in aerated waters were not 
electrolytically cleaned because of the 
resulting instability of the open circuit 
potential (Ecorr)- ^ series of test runs 



was made with EX-TEN-H60 steel in Magmont 
water to determine variation of the open 
circuit cell potential (corrosion poten- 
tial) and corrosion rate, the latter as a 
function of the time interval in which 
the specimen was in solution prior to 
initiation of linear polarization tests. 

Total immersion, weight-loss determin- 
ation of corrosion rates from static 
tests was based on ASTM Standard G31-72, 
"Laboratory Immersion Corrosion Testing 
of Metals" (_5 ) . Specimens of EX-TEN- 
H60 and KAI-WELL-55 steels were machined 
from sheet stock to approximately 1 in 
square, and a 0.082-in-diam hole was 
drilled in each specimen for suspension 
in the test solution. The specimens were 
ground over 120-grit SiC paper, dimen- 
sions were measured, and surface areas 
calculated. They were then ultrasonical- 
ly cleaned in ethanol and weighed. Two 
specimens of each steel were suspended 
with nylon line in each mine water. The 
four lead mine waters were contained in 



1,000-mL beakers immersed in a constant- 
temperature bath at 62° ±0.5° F. The tem- 
perature of 62° F was the average temper- 
ature of the lead mine waters , which 
ranged from 61° to 64° F. The beaker 
containing the iron mine water was im- 
mersed in a separate constant-temperature 
bath, which was maintained at 80°±0.5° F, 
the in-mine water temperature. Test so- 
lution temperatures were monitored daily. 
Dissolved oxygen contents were measured 
daily for the first few days and weekly 
thereafter for the duration of the test. 
No attempt was made to control dissolved 
oxygen content. The beakers were covered 
loosely to permit access of air. The 
total-immersion tests were terminated at 
2,900 h. The specimens were rinsed and 
scrubbed with a bristle brush under run- 
ning water to remove loosely adherent 
corrosion products, dried in a warm air 
blast, and weighed. Corrosion rates were 
calculated from weight losses. 



RESULTS AND DISCUSSION 



Results of chemical analyses of the 
HSLA steels used for the manufacture of 
Split Sets are shown in table 1. The EX- 
TEN-H60 composition was within specifica- 
tions (12). No analysis was performed 
for the nonspecified elements of sulfur, 
phosphorus, and copper, nor for nitrogen. 
The composition of KAI-WELL-55 steel 
was within specifications (7) for those 



elements for which analyses were per- 
formed. No analyses were conducted on 
KAI-WELL-55 steel for the specified minor 
elements of sulfur and phosphorus. Re- 
sults of analysis of the Swellex steel, 
in weight-percent, are as follows: C, 
0.06; Mn, 0.24; Si, <0.05; S, 0,02; P, 
<0,01; and balance Fe. 



TABLE 1. - High-strength, low-alloy steel compositions, weight percent 



Element 


EX-TEN-H60 


KAI-WELL-55 




Specification' 


Analysis 


Specif ication^ 


Analysis 


C 


Max 0.25 

0) 
NS 

Max 1.35 

Max .012 

NS 

NS 

NS 

(^) 


0.23 

.01 

NA 

1.22 

NA 

NA 

NA 

<.02 

.01 


0.2 -0.3 

NS 

Min .20 

.85-1.30 

NS 

Max .05 

Max .05 

Max .12 

NS 


0.3 


Cb 


NA 


Cu 


32 


Mn 


1 . 12 


N 


NA 


P 


NA 


S 


NA 


Si 


<.02 

NA 


V 





NA Not analyzed. 
NS Not specified. 
'Woldman (12), p. 435. 



^Ingersoll-Rand Co. (_7 ) . 

^Specification minimum 0.02 wt pet Cb + V, 



Analyses of mine waters are shown in 
table 2. All of the waters were somewhat 
basic, with pH values of 8.0 or 8.1. 
Calculated Langelier indices of -0.2 to 
+0.5 indicate little tendency toward car- 
bonate precipitation for any of the five 
mine waters. The Pea Ridge water con- 
tains relatively large amounts of Na"*", 
S04"2, and HC03~ ions, as reflected in 
the large amount of total dissolved sol- 
ids. The Magmont and Indian Creek waters 
are much higher in CI" ion content than 
the other waters, and the Magmont water 
is also relatively high in HC03~ ion con- 
tent. All of the waters analyzed low in 
iron contents, <0.1 ppm Fe. 

Shown in figures 1 and 2 are exam- 
ples of anodic and cathodic polarization 
plots, respectively, from which Tafel 
constants (slopes) are calculated. The 
plots were generated from a deaerated 
lead mine water and Split Set steel sam- 
ples. Corrosion current and subsequently 
general corrosion rate are calculated 
from the slope of a polarization resist- 
ance (linear polarization) plot and the 
Tafel constants. An example of a pol- 
arization resistance plot obtained with 
deaerated lead mine water and a Split Set 
steel sample is shown in figure 3. 

Results of the series of electrochemi- 
cal tests to determine effects on the 
apparent corrosion rate of specimen sta- 
bilization times are shown in figure 4. 
Apparent corrosion rates of specimens 
in either electrolytically cleaned or 
abraded only (600-grit SiC paper and 
ultrasonically cleaned in ethanol) con- 
ditions stabilized quickly in deaerated 
water. Apparent corrosion rates of 
abraded specimens also stabilized quickly 
in air-saturated water. However, elec- 
trolytic cleaning of specimens tested in 




CURRENT, nA/cm^ 

FIGURE 1.- Example of anodic polarization plot. 
Deaerated lead mine water and HSLA steel. 



. -.80 h 

z 



o 

a. -.90 - 



1 


1 




1 








~ 








- 


1 


1 




NX 

1 





10' 



10= 



CURRENT, nA/cm^ 

FIGURE 2. • Example of cathodic polarization plot. 
Deaerated lead mine water and HSLA steel. 

air-saturated water resulted in very un- 
stable apparent rates for the first few 
minutes of immersion. Corrosion rates 
were relatively stable in all cases after 
immersion for ~4 min. Corrosion rates 
reported in table 3 for electropolished 
specimens in air-saturated waters were 
obtained with specimens that had been 
cleaned by abrasion only. All other 



TABLE 2. - Analyses 


of mine 


waters 


from 


Missouri le 


ad and iron 


mines 




Contents, ppm 


pH 




Mine 


Cations 


Anions 


Total 
dissolved 
solids 


Langelier 




Ca 


K 


Mg 


NA 


CI 


HCO3 


SO4 


index 


Fletcher 


13 
33 
22 
18 
16 


0.8 
5.4 
.5 
2,0 
3,8 


22 
21 
26 
19 
16 


3.4 
39 

1.3 
12 
198 


24 

105 

105 

26 

29 


194 
226 
269 
213 
255 


86 

26 

62 

101 

127 


265 
451 
438 
321 
565 


8.1 
8,1 
8.0 
8,0 
8,0 


-0.2 


Indian Creek 


+,5 


Magmont 

St. Joe #28 

Pea Ridge ' 


+ .2 
+.3 
+ .4 



'iron mine; others lead mines. 



..;.-:t-i ^i?EH:::5g5JU?ii3iS?H^Mii^Sia^il 



-0.68 



-.70 - 



-.72- 



-.74 



-10 




CURRENT, nA/cm^ 

FIGURE 3. - Example of polarization resistance 
(linear polarization) plot. Deaerated lead mine wa- 
ter and HSLA steel. 



rates were determined on specimens that 
had been electrolytically cleaned. 

Results of electrochemical corrosion 
tests, shown in table 3 (standard devia- 
tion denoted by sjoabol a), indicate that 
KAI-WELL-55 steel exhibits, on the aver- 
age, slightly lower corrosion rates than 
EX-TEN-H60. Such a difference was also 
observed in corrosion studies of these 



KEY 




soturoted water 


Deaerated water 


Electrolytically 


• Electrolytically 


cleaned 


cleaned 


Abroded 


■ Abraded 



TIME , min 

FIGURE 4. - Exampleof derived electrochemical 
corrosion rate versus stabilization time for EX- 
TEN-H60 steel in a lead mine water. 

steels in western copper and uranium mine 
waters (11). Galvanized steel exhibited 
much lower rates in deaerated waters than 
either of the two HSLA steels. In aer- 
ated waters, however, passivation of both 
EX-TEN-H60 and KAI-WELL-55 resulted in 
much lower rates than those of galvanized 
steel, except in the Pea Ridge water. 
Passivation was observed only in certain 
electrochemical tests and was not evident 
in the gravimetric tests. It may there- 
fore not be a significant factor for the 
longer term exposure of installed roof 
bolts. Rates of 17.6 and 11.6 mpy for 
EX-TEN-H60 and KAI-WELL-55, respectively, 
in aerated Pea Ridge water were the high- 
est observed. Also, rates for the two 
steels in deaerated water from this iron 



TABLE 3. - Electrochemically determined corrosion rates 



Mine water 



Test 

solution 

temperature. 



Oxygen 
content, ' 
ppm 



Corrosion rate,^ mpy 



EX-TEN-H60 



Av 



KAI-WELL-55 



Av 



a 



Galvanized 



Av 



Fletcher, . . . , 
Indian Creek, 

Magmont , 

St. Joe #283, 
Pea Ridge*.., 



63 
63 
62 
62 
61 
61 
64 
64 
80 
80 



0.4 
9.4 

.5 
9.4 

.4 
9.6 

.5 
9.3 

.3 
7.5 



2.7 

.3 
1.6 

.2 
1.8 

.2 
1.6 

.4 

2.8 

17.6 



0.7 

.1 

.2 

.05 

.3 

.1 

.4 

.1 

.3 
6.1 



1.4 

.2 
1.5 

.4 
1.6 

.1 
1.4 

.2 

2.1 

11.6 



0.2 

.02 

.2 

.02 

.2 

.04 

.4 

.02 

.1 
3.3 



0.5 
2.3 

.3 
3.8 

.5 
1.6 

.6 
2.3 

.4 
1.6 



0.1 
.8 
.05 
.5 
.1 
.2 
.1 
.9 
.1 
.4 



'Higher values are aerated; those at 0.5 ppm or less are deaerated. 
^o is standard deviation. 

^For same conditions, indicated rates for Swellex steel were 0.1 mpy (deaerated) 
and 0.2 mpy (aerated). 

*Iron mine; others lead mines. 



- 



1 


1 I 


1 1 


1 




^ 


^"^y^-V 


/ _ 


- 






- 


E corr^ 


1 1 


1 1 


1 



10^ 10" 10° 

CURRENT, nA/cm^ 



FIGURE 5. - Example of pitting scan showing 
little tendency of specimen to pit. 



1 


III! 


I 


- 


Ec— (^ / 


- 


E corr N^ 


~.=^^ ^/>*^ 


1 




' ~-- -^ — — 


1 


1 1 1 1 



10^ 10^ 

CURRENT, nA/cm 



0= 10" 

2 



FIGURE 6. - Example of pitting scan indicating 
tendency of specimen to pit. 



mine were higher than rates obtained in 
the deaerated waters from the lead mines. 

Limited electrochemical tests on Swell- 
ex bolt steel resulted in indicated cor- 
rosion rates lower than those obtained 
with EX-TEN-H60 or KAI-WELL-55 steels. 
In deaerated St. Joe #28 water, a rate 
of 0.1 mpy (a = 0.02) was observed with 
Swellex steel compared with rates of 1.6 
and 1.4 mpy for EX-TEN-H60 and KAI-WELL- 
55 steels, respectively, in the same wa- 
ter. Similarly, in aerated St. Joe #28 
water, a rate of 0.2 mpy (a = 0.03) was 
obtained for Swellex steel compared with 
rates of 0.4 and 0.2 mpy for EX-TEN- H60 
and KAI-WELL-55, respectively. 

Corrosion rates determined by the long- 
term, static weight-loss method are shown 
in table 4. The slightly lower electro- 
chemical corrosion rates of KAI-WELL-55 
steel compared with those of EX-TEN-H60 
steel were not evident in the weight-loss 
tests except in Pea Ridge water, where 
KAI-WELL-55 steel averaged 1.6 mpy and 



EX-TEN-H60 averaged 2.3 mpy. The highest 
rate observed in the weight-loss tests 
was 2.8 mpy for KAI-WELL-55 steel in 
Fletcher water. Corrosion rates deter- 
mined with weight-loss tests in waters 
containing from 6.3 to 7.2 ppm dissolved 
oxygen (from air dissolution) were com- 
parable with electrochemically determined 
rates in deaerated mine waters containing 
only 0.3 to 0.5 ppm dissolved oxygen. 
Apparently, rates determined electrochem- 
ically in deaerated waters are somewhat 
more indicative of long-term corrosion 
rates than those electrochemical rates 
obtained in air-saturated waters. Pas- 
sivation was not evident in the static 
tests, although it may have been a tran- 
sient occurrence early in the tests on 
relatively clean surfaces before substan- 
tial rust products began to form. 

Typical pitting scans of the HSLA and 
galvanized steels are shown in figures 5 
and 6. Figure 5 is a scan indicating 
little tendency of the specimen to pit. 



TABLE 4. - Corrosion rates determined by weight-loss method 





Test 

solution 

temperature, 

°F 


Oxygen 

content , 

ppm 


Corrosion 


rate, mpy 


Mine water 


EX-TEN-H60 


KAI-WELL-55 




Av 


a 


Av 


a 


Fletcher 

Indian Creek. . . . 
Magmont 


62 
62 
62 
62 
80 


6.3 
6.4 
7.2 
6.7 
6.6 


2.1 
2.4 
1.8 
2.6 
2.3 


0.2 
.3 
.3 
.3 
.4 


2.8 
2.7 
1.6 
2.3 
1.6 


0.5 
.2 
.8 


St. Joe #28 

Pea Ridge! 


.2 
.04 



^Iron mine; others lead mines, 



.-.:..r^^--^.~.:^.i<''^:r^.fr:v?.^i^^^^^ 



TABLE 5. - Pitting tendency of HSLA and galvanized steels 
in Missouri mine waters 



Mine 



EX-TEN-H60 KAI-WELL-55 Galvanized 



PITTING TENDENCY— DEAERATED 



Fletcher. . . . , 
Indian Creek, 

Magmont , 

St. Joe #28.. 
Pea Ridge 1 , , . 




PITTING TENDENCY— AERATED 



Fletcher. . . . , 
Indian Creek, 

Magmont 

St. Joe #28.. 
Pea Ridge ^ . . , 




ND Not determined. Mod Moderate, 
'iron mine; others lead mines. 



If the protection potential (Ep) is more 
positive than the corrosion potential 
(E^Q^^), as it is in figure 5, pitting 
becomes less likely to occur (4^, 6^) as E- 
becomes more positive relative to E^q^j.. 
Ej.Qj.j. is the open-circuit potential. The 
protection potential E is defined as the 
potential at which the hysteresis loop of 
the pitting scan is completed and below 
which (E more negative) pits will not 
initiate. Figure 6 is a typical plot in 
which the protection potential is more 
negative than the corrosion potential and 
pitting of the specimen is indicated. 
The pitting potential (E^,, also referred 
to as the critical potential) has also 
been used as an indication of pitting 
tendency, but the protection potential is 
more reproducible and is now considered a 
more reliable indicator (6), The pitting 
potential is defined as the potential at 
which the current increases rapidly and 
above which (E more positive) pits will 
initiate and grow. Research has been 
done (8^) which indicates that, when pit 
initiation time is considered, E^, = E . 

Results of the evaluation of pitting 
scans are shown in table 5. Pitting 



tendency was evaluated on the basis of 
difference between E^^^^ and E . If Ep 
was more negative than E^^^^, pitting 
tendency was rated as high. When Ep 
was somewhat more positive than E^^^^, 
but the difference between E^^^^ and Ep 
remained in the range to 0.1 V, the 
pitting tendency was arbitrarily rated 
as moderate. Similarly, with Ep more 
positive than E^.^^^, a difference be- 
tween E^Qpp and Ep greater than 0.1 V was 
rated as an indication of low tendency 
to pit. 

Moderate to high pitting tendency is 
indicated for both HSLA steels in all of 
the air-saturated waters. Passivation of 
the steels in air-saturated waters during 
electrochemical testing also indicates a 
probable tendency to pitting, since this 
is a common occurrence on metals that 
passivate. A high tendency to pitting is 
indicated for galvanized steel in the de- 
aerated waters, as well as aerated Indian 
Creek and Pea Ridge water. Evaluation of 
the scans indicates a high pitting ten- 
dency for both HSLA steels and galvanized 
steel in Pea Ridge water in aerated and 
deaerated conditions. 



CONCLUSIONS 



Based on results of total-immersion, 
weight-loss corrosion tests, there is 
little difference in corrosion rates be- 
tween EX-TEN-H60 and KAI-WELL-55 steels 
in Missouri lead and iron mine waters. 
Slightly lower rates were observed for 



copper-bearing KAI-WELL-55 steel than for 
EX-TEN-H60 in electrochemical tests. 

Galvanized steel exhibits much lower 
rates in electrochemical tests in de- 
aerated water (<0.5 ppm dissolved oxygen) 
than either of the HSLA steels. 



Passivation effects observed in elec- 
trochemical tests in air-saturated (>9.3 
ppm dissolved oxygen) lead mine waters 
resulted in very low rates of 0.4 mpy 
or less for both HSLA steels. Passiva- 
tion probably does not occur in bolt- 
rock contact areas of installed stabiliz- 
ers , owing to lack of oxygen. It may 
occur on bolt surfaces exposed to am- 
ple air and moisture; but, if it occurs 
on installed stabilizer surfaces, this 
may be a transient effect for relatively 
clean surfaces as opposed to rusting 
surfaces. In the electrochemical tests, 
passivation was not observed on either 
of the HSLA steels in the iron mine wa- 
ter. Passivation was also not evident 
for the two HSLA steels in any of the 
waters for the total-immersion condi- 
tions of atmospheric oxygen dissolution, 
although it may have occurred to some 
extent early in these weight-loss tests 



when the surfaces were relatively free of 
rust products. 

Corrosion rates determined by the long- 
term weight-loss tests in water at at- 
mospheric oxygen saturation are more com- 
parable with rates determined electro- 
chemically in deaerated water than with 
electrochemically determined rates in 
air-saturated water. 

Limited electrochemical tests on Swell- 
ex stabilizer steel indicated corrosion 
rates generally of the same order of mag- 
nitude as those obtained with the HSLA 
steels used for Split Set stabilizers. 

Moderate to high pitting tendency was 
observed for both HSLA steels in all air- 
saturated mine waters. Galvanized steel 
exhibited a high tendency to pit in all 
deaerated waters. Pitting tendency was 
high for both of the HSLA steels and the 
galvanized steel in either the deaerated 
or air-saturated iron mine water. 



REFERENCES 



1. Ailor, W. H. Handbook on Corrosion 
Testing and Evaluation. Wiley, 1971, 873 
pp. 

2. American Society for Metals. Met- 
als Handbook. Cleveland, OH, 1948, 1,332 
pp. 

3. . Metals Handbook. Proper- 
ties and Selection: Nonferrous Alloys 
and Pure Metals. Metals Park, OH, 9th 
ed. , V. 2, 1979, 855 pp. 

4. American Society for Testing and 
Materials. Standard Practice for Con- 
ducting Cyclic Potentiodynamic Polariza- 
tion Measurements for Localized Corro- 
sion. ANSI/ASTM G61-78 in 1982 Annual 
Book of ASTM Standards: Part 10, Met- 
als - Physical, Mechanical, Corrosion 
Testing. Philadelphia, PA, 1982, pp. 
1,124-1,129. 

5. Standard Recommended Practice for 
Laboratory Immersion Corrosion Testing 
of Metals. 031-72 in 1982 ASTM Stan- 
dards: Part 10, Metals - Physical, Me- 
chanical, Corrosion Testing, Philadel- 
phia, PA, 1982, pp. 959-970. 

6. Baboian, R. , and G. S. Haynes. 
Cyclic Polarization Measurements - Exper- 
imental Procedure and Evaluation of Test 
Data. Ch. in Electrochemical Corrosion 
Testing, STP 727, ed. by F. Mansfeld and 
U. Bertocci, ASTM, 1981, pp. 274-282. 

irU.S CPO: 1985-605-017/20,126 



7. Ingersoll-Rand Co. research staff. 
Private communication, July 1981; availa- 
ble upon request from M. M, Tilman, Bu- 
Mines, Rolla, MO. 

8. Kruger, J. New Approaches to the 
Study of Localized Corrosion. Ch. in 
Electrochemical Techniques for Corrosion, 
ed, by R. Baboian, Nat, Assoc, Corrosion 
Eng,, Katy, TX, 1977, pp, 35-41, 

9. Lusignea, R, , J, Felleman, and G, 
Kirby, Development of a Nondestructive 
Test Device for Friction Rock Supports 
(contract H0202030, Foster-Miller, Inc.). 
BuMines OFR 165-83, 1983, 135 pp.; NTIS 
PB 83-257519. 

10. Peterson, W. M. , and H. Siegerman, 
A Microprocessor-Based Corrosion Mea- 
surement System, Ch, in Electrochemi- 
cal Corrosion Testing, STP 727, ed. by 
F. Mansfeld and U. Bertocci. ASTM, 1981, 
pp. 390-406. 

11. Tilman, M. M. , A, F, Jolly III, 
and L, A, Neumeier, Corrosion of Fric- 
tion Rock Stabilizers in Selected Uranium 
and Copper Mine Waters, BuMines RI 8904, 
1984, 23 pp, 

12. Woldman, N, E., and R. C. Gibbons, 
Engineering Alloys, Van Nostrand Rein- 
hold, 5th ed., 1973, 1,427 pp. 



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